Dual nip multi-feed detection and control system

This is a divisional of U.S. application Ser. No. 13/017,081 filed Jan. 31, 2011 by the same inventors, now U.S. Pat. No. 8,280,263, and claims priority therefrom. This divisional application is being filed in response to a restriction requirement in that prior application.

1. Field of the Disclosure

This invention relates in general to an image forming apparatus, and more particularly, to an image forming apparatus including a system that that is capable of detecting and separating multi-fed sheets whilst allowing individual single sheets to continue feeding.

2. Description of Related Art

Multi-feeds continue to be a problem when separating and feeding sheets from a stack of sheets within the sheet handling industry. A multi-feed occurs when two or more sheets are fed at once and can cause several problems. Typically, a multi-feed will jam somewhere in a machine, either due to the sheets not moving “as one” or timing issues as the sheets aren't exactly on top of one another so the length of the fed sheet appears longer than the machine expects. If the sheets make it through the whole machine the user can find blank sheets within large print runs, or in the case of duplex printing blank sides. All representations of multi-feed are an annoyance to the user and costly in terms of wasted paper and toner on jobs that need to be re-run, the extra electricity consumed in re-running jobs and the cost of time spent by the user either clearing the jam or re-running the jobs. Reducing the number of multi-feeds experienced will improve the overall user experience. Multiple solutions have been advanced for detecting and separating them. Most of the solutions are only capable of dealing with two sheets fed together.

For example, in U.S. Pat. No. 2,892,629 an arrangement is shown in which one of the two rollers between which the sheets pass is positively driven, but the other roller is a retard roller and is not positively driven. The latter roller is freely rotatable on a shaft and is spring urged to turn in a direction opposite to that of the positively driven roller. When only one sheet is passing between the two rollers, the friction is such as to cause the retard roller to turn in the direction of motion of the sheet and against the spring bias. However, when two sheets are disposed between the two rollers, the first sheet, bearing against the positively driven roller, is advanced while the second sheet is moved to the rear, under the influence of the spring biased retard roller which now rotates in the opposite direction to sheet transfer. U.S. Pat. No. 3,895,790 also uses a retard roller arrangement in which the retard roller is reversed when a multiple feed occurs. The prior art devices use a slip clutch system to provide forward movement when a multiple feed is not present. All of these devices depend upon the relative friction between the positively driven roller and the sheet to be advanced as being greater than the friction between the sheet to be advanced and the sheet or sheets to be returned. In U.S. Pat. No. 4,060,232 a garter spring drive is used to rotate a retard roll in a sheet reversing direction when multiple sheets are in a nip formed by a retard roll and a positively driven separator roll. When one sheet is in the nip, slippage occurs between the garter spring and pulleys so that the retard roll turns with the separator roll in a paper feed direction. All of the patents mentioned hereinbefore are included herein by reference.

Even though these solutions are useful, there is still a need for a multi-feed system that will facilitate detection and separation of more than two sheets while reliably feeding sheets one at a time.

Accordingly, a system is disclosed that detects multi-feeds and separates all sheets allowing a single sheet to continue into the machine. The system includes a nip with a standard drive roller for feeding sheets. A reversible pressure roller downstream of the drive roller idles in the direction of the paper feed in normal operation. When a multi-feed is detected, the pressure roller is turned ON using appropriate timing. This roller has more friction with the sheet in its contact than the friction between sheets. This drives the sheet in contact backwards. This sheet can be diverted to a separate paper path using a gate mechanism and, if desired, fed back into the sheet stream or feed path.

Various of the above-mentioned and further features and advantages will be apparent to those skilled in the art from the specific apparatus and its operation or methods described in the example(s) below, and the claims. Thus, they will be better understood from this description of these specific embodiment(s), including the drawing figures (which are approximately to scale) wherein:

FIG. 1 is a frontal view of a schematic diagram of an alternative multi-feed detection and control system of the present disclosure;

FIG. 2 is a flow chart describing system operation; and

FIG. 3 is a configuration for multi-feed detection and separation in accordance with the present disclosure.

Referring now to FIG. 1 , a conventional electrostatographic machine or printer is represented by block 8 . It includes a charge receptor or photoreceptor having an imageable surface and rotatable in a predetermined direction to be uniformly charged by a charging device and imagewise exposed by an exposure device to form an electrostatic latent image on the surface. The latent image is thereafter developed by a development apparatus that, for example, includes a developer roll for applying a supply of charged toner particles to the latent image. The charged toner particles adhere to appropriately charged areas of the latent image. The surface of the photoreceptor then moves to a transfer zone. Simultaneously, a print sheet onto which a desired image is to be printed is drawn from a sheet supply stack of a sheet feeding system and conveyed along a sheet path to the transfer zone.

At the transfer zone, the print sheet is brought into contact with the surface of the photoreceptor, which at this point is carrying toner particles thereon. A corotron at the transfer zone causes the toner image on the photoreceptor to be electrostatically transferred to the print sheet. The print sheet is then forwarded to subsequent stations, as is familiar in the art, including a fusing station to fuse the image to the copy sheet and then to an output tray. The reproduction machine 8 includes a controller or electronic control subsystem (ESS) which is preferably a programmable, self-contained, dedicated mini-computer having a central processor unit. As such, it is the main control system for components and other subsystems including paper feeding in machine 8 .

In further reference to FIG. 1 , the multi-feed detection and control system 100 is illustrated in detail and is adapted to detect multi-feeds and separate all sheets while allowing a single sheet to continue into machine 8 . As illustrated, multi-feed detection and control system 100 includes a paper path C through which media, including sheets of all types, are conveyed to receive images thereon. A paper or sheet detection sensor S 2 is positioned at an entry point A for paper entering a first drive roll nip 103 formed by drive roll 101 and idler roll 102 , a second drive roll nip 112 formed by drive roll 110 and reversible roll 111 powered by motor M 2 , and a third drive roll nip 122 formed by drive roll 120 and idler roll 121 . Drive roll 101 has a motor M 1 drivingly connected thereto which also drives rolls 110 and 120 in the direction of paper feed. A multi-feed detection sensor 51 is shown positioned downstream of drive nip 112 and upstream of drive nip 122 . Multi-feed sensor S 1 is preferably an optical sensor; however, any conventional sensor could be used, if desired.

A gravity gate 130 positioned in paper path C, such that, it allows paper to pass under it in the paper feed direction and pass over it in the direction of exit point B when multi-feeds are detected. Ordinarily, drive roller 110 is ON and rotating in the paper feed direction, while reversible roller 111 attached to motor M 2 idles against it. When a multi-feed is detected by S 1 , motor M 2 is turned ON which causes roller 111 that is attached to it to rotate in the opposite direction to the paper feed direction. Roller 111 has greater friction with the paper than between the paper sheets, so when a dual-feed occurs roller 111 attached to motor M 2 has enough friction to drive the upper sheet backwards into gravity gate 130 while the lower sheet continues to move in the forward direction. The trail edge of the multi-feed must pass gravity gate 130 to allow it to drop before motor M 2 is turned ON, therefore, when the multi-fed sheet is fed backwards it exits from the system at point B. To ensure that the remaining “single” sheet is not fed in the wrong direction, roller 111 must have a lower coefficient of friction than drive roller 110 feeding the paper in the correct direction. An advantage to this configuration is that through experimentation it has been found that roller 111 rotating in the opposite direction to the paper feed direction will feed out a single sheet at a time until there is only one remaining which then carries on in the correct direction. Thus, when more than two sheets are fed, roller 111 rotating in the opposite direction to the paper feed direction will feed out a single sheet at a time to exit point B until there is only one remaining which then carries on in the sheet feed direction. Sheets exiting point B can either be conveyed to an output tray or re-fed into paper path C past entry point A to receive images thereon.

A flow chart 200 is shown in FIG. 2 which describes the system operation. That is, in its initial state, sensors S 1 and S 2 in blocks 202 and 205 , respectively, are Low and motors M 1 and M 2 in blocks 207 and 209 are OFF. But once the start button 201 is pushed, sheets are fed from a paper supply (not shown) and motor M 1 in block 210 is turned ON. Paper is fed in block 212 , sensor S 2 in block 214 is High, sensor S 1 in block 216 is High and sensor S 2 goes Low in block 218 because in the environment tested (feeding A 4 long edge sheets) sensors S 1 and S 2 were about 200 mm apart, and thus, the trail edge of a sheet would pass through sensor S 2 before the system had made a decision. In decision block 220 , if no multi-feed is detected sensor S 1 is Low and motor M 1 is turned OFF in block 224 . The job is finished in block 240 . However, if a multi-feed is detected in decision block 220 , a delay T 1 is introduced in block 226 following sensor S 2 going low in order to allow for the trail edge of the sheet to pass gravity gate 130 . Afterwards, as shown in block 228 , motor M 2 is turned ON for a predetermined time T 2 in order to feed sheet multi-feeds backwards and out of exit point B. Subsequently, motor M 2 is turned OFF in block 232 , sensor S 1 is now Low at block 234 and motor M 1 is OFF in block 224 as the lowermost sheet in the multi-feed continues to feed and the job is finish at block 240 . If desired, sensor S 1 could be omitted and instead a multi-feed sensor placed anywhere prior to the entry point A.

An embodiment 300 of the present disclosure is shown in FIG. 3 that eliminates the need for gravity gates, but still operates under the same principles of FIG. 1 . This configuration includes tri-rollers 301 , 302 and 303 positioned upstream of drive roll 305 and reversible roll 307 . The tri-rollers are in frictional or geared contact with each other, to provide two spaced-apart nips, one being an input nip formed by rollers ( 302 , 303 ) to an associated paper path to a downstream imaging device, and the other being an output nip formed by rollers ( 301 , 302 ) for extracting each sheet of a multi-feed except the uppermost sheet from the paper path. A motor M 8 is drivingly attached to drive roll 302 and drive roll 305 . A motor M 9 is attached to reversible roller 307 . The entry point into the system is at E and sheets are directed into paper path F for conveyance to an image transfer station (not shown). When a multi-feed is sensed by sensor S 1 , reversible motor M 9 is actuated and the lower sheet is fed backwards in the direction of arrow G after the trail edge has dropped down while the upper sheet continues through the system (paper path F) after a predetermined pause for sheets below it to be purged.

In recapitulation, a multi-feed detection and control system has been disclosed that comprises structure and methods configured to separate multi-fed sheets conveyed in a paper path and re-feed the separated sheets into the paper path or drive them into a purge tray. The system includes a reversible roll that idles on a driver roll in the direction of paper feed when single sheets are conveyed, but when a multi-feed is detected the reversible roll is actuated to reverse rotation and drive all sheets above a lowermost single sheet in a reverse and exit direction while the lowermost sheet is delayed for a predetermined time and then fed in the paper feed direction. The system is compatible with paper paths that are vertical, horizontal or inclined at predetermined angles, and it should also be understood that the system could equally be used on any device that feeds media, and not necessarily for marking media, e.g., in automatic teller machines.

The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others. Unless specifically recited in a claim, steps or components of claims should not be implied or imported from the specification or any other claims as to any particular order, number, position, size, shape, angle, color, or material.